The Institute of Electrical and Electronics Engineers (IEEE) has incorporated a modulation format for pulse amplitude modulation (PAM4) into optical networking standards (e.g., 802.3bs for 400 Gb/s, and 802.3cd for 200/50 Gb/s) to address continuously rising bandwidth capacity. Adoption of PAM4 modulation increases the single lane bandwidth by a factor of two. However, further increasing the bandwidth and/or squeezing the form factor has resulted in a bottleneck.
Ribbon solutions (e.g., 400GBASE-DR4, 100G-PSM4, 100GBASE-SR4) may be defined and used for high bandwidth connections, especially for intra-data center (e.g., up to 2 km). However, duplex solutions remain viable for both inter-data-center and intra-data-center connections, on both single mode fiber (SMF) and multi-mode fiber (MMF). IEEE solutions to maintain duplex interfaces tends to assume the adoption of multiple wavelength in Coarse Wavelength Division Multiplexing (CWDM) or Local Area Network (LAN) Wavelength Division Multiplexing (LWDM) grids.